UNIT 2 - NEURONS Flashcards
What do neurones consist of?
Remember: NEURONE IS THE BASIC FUNCTIONAL UNIT OF THE NERVOUS SYSTEM
Cell body, dendrites, axon, and presynaptic terminal.
Also consist of the cell, glia (support cell), neuroglia
Main function of neurone:
a) receive and process information from sensory receptors and other neurons
b) send information to the next neuron in the chain of communication or non-neuronal structure (effector organs)
Cell body:
Neuron consists of: Cell body (soma) Dendrites Axon Presynaptic terminal
Dendrites
Synaptic receptors: dendrites receive information from another neuron
Dendritic spine: to increase synapse
Axon
> Diameter, carries neural impulse toward other neurons, organ or muscle
Covered in myelin sheath
Nodes of Ranvier
Only one axon
Glia
> There are as many glia as neurons
> Does NOT transmit information
Glia (Astrocytes)
Astrocyte: wraps around the synapse of functionally related neurons
Other cells of Glia:
- Microglia
- Oligodendrocytes
- Schwann cell
- Radial Glia
- Microglia:: immune system, removing fungi and viruses in the brain.
- Oligodendrocytes: CNS
- Schwann cell: PNS construct the myelin sheath
- Radial Glia: guide the migration of neurons and their axons during embryonic developement
Ions
When electrolytes are dissolved in water, they split into two parts each with an opposing electrical charge
Ions force of act:
They move in certain direction > positive and negative it’s called ELECTRICAL POTENTIAL
Force1) Electostatistic pressure: when ions move toward the opposite electrical charge. (e.ie a positive charged ion will move toward areas of negativity)… ALSO CALLED ELECTRICAL GRADIENT
Force 2) DIFFUSION cause ions to move toward are of relatively lower concentration (i.e an ion will go to areas where there are fewer than ions) ALSO CALLED CONCENTRATION GRADIENT
Membrane Potential
The difference in electrical charge between the inside of the cell and outside of the cell
Resting Potential
DIFFERENCE BETWEEN INSIDE + OUTSIDE : IS RESTING POTENTIAL
Axon membrane is semi-permeable = conducting properties
- Positive on the outside / Negative on inside
- Due to unequal ion distribution across membrane
- Alway -70 millivolts (mV)
Resting Potential - imoportant IONS:
Sodium (NA+)
Potassium (K+)
Chloride (CI-)
Calclium (Ca2+)
Resting potential - inside vs outside
> There is more Na+ (sodium-) outside, meaning inside is then negative.
At rest more K+ inside.
Equlibrium when only few K+ leave the membrane
> They leak across SODIUM-POTASSIUM PUMP: to ensure that high concentration of Na+ outside of cell and high concentration of K+ is inside of cell.
What keeps negitevly charge protein inside?
Organis onions (A-) = they keep the inside negative A- Can't pass through a cell
Chloride Ions:
> more outside
want to diffuse inside cell
little movement
Hyperpolarisation
Negative charge pushes the membrane potential further toward negative
Depolarisation
A small positive charge become positive. (toward zero mV)
- but after weak stimulation membrane returns back to resting potential (-70mV)
Massive depolarisation:
- Threshold of excitation
- Voltage-gate
- Action Potential
When it reaches the threshold,
Ion channel open activating membrane > VOLTAGE-GATE CHANNEL
When it reaches threshold, voltage-gated NA+ channel open causing influx of NA+ - then it shoots up to more positivity, this is ACTION POTENTIAL
The All-or-None law
All depolarisation when it reaches threshold of excitation
Action Potential
REVERSED: Inside is positive than outside
Repolarisation and Hyper polarisation
When the threshold of exciation is reached voltage-gate K+ channel also open
- K+ opens slightly later and moves more toward negative (given that the inside is positive)
- K+ takes their positive charge with them
Also, Voltage gate Na+ channel close at the peak of the action potential: Na+ are stopped from entering cell and making it positive
Turning back to negative is REPOLARISATION:
> allow k+ to be open for a while, causing hyperpolarisation: more negative than it was during resting potential
> K+ channels close again > Goes to resting potential
By the help of sodium-potassium pump.
Refractory Period
After repolarising, the cell is less likely to produce another action potential, that is REFRACTORY PERIOD
Absouloute refractory period: impossible to produce another action (1-2 ms)
Relative refractory period: needs larger stimulation than normal to produce action potential (2-3ms)
Propagation of Action Potential
Na+ flow inside the axon to the neighboring areas of negativity
- does not go backward
Saltatory Conduction
When Na+ goes to one of nodes of ranviar to the other one (salta=jump)
Effecient because:
- It speeds up propergation of action potential
- Maintains strength of the neural impulse
- Conserves energy
Multiple sclerosis
Immune system that attacks myelin sheat (autoimmune disease)
The synapse
Gap or junction bewteen neuron allowing them to communicate
- Communcation: PRE-SYNAPTIC
- Recieving: POST-SYNAPTIC
Light stimulation of PRE > depolorises > POST: GRADED POTENTIAL
EPSPs VS IPSPs
EPSPs
> DEPOLARISATION IS AN EXCIATORY POSTSYNAPTIC POTENTIAL
>NA+ to POSTsynaptic membrane
> Increase the postsynaptic to fire
IPSPs:
> INHIBITORY POST SYNAPTIC POTENTIAL:
> WHEN PRESYNAPTIC neuron cause hyperolatisation to POST
> Decrease the postsynaptic to fire
So it all comes down which neuron fires is determined by
TEMPORAL SUMMATION VS SPATIAL SUMMATION
Temporal summation: EPS adding depolorasation to another EPSP
Spatial summation: when several presynaptic neuron stimulate a postsynaptic neuron
Loewl (1920)
Frogs release chemical of: neurotransmitters
Neurotransmitter synhesis: GABA VS GLUTAMATE
Most synaptic communcation is done by Glutamate (excitatory) and GABA (inhibitory)
> both amino acid in neurotransmitter
Neurotransmitter released
Action potential travel down axon to the presynaptic terminal where they activate:
VOLTAGE-GATE CALCIUM (CA2+) channel causing and influx of CA2+
Removal of neurotransmitter
Achethycholine is broke down into inactive fragment (acetate and choline) by ACETHYCHOLINSTERASE
REPUTAKE
Not broken neurotransmitter, but rather reabsourbed
Negative feedback to presynaptic neurone for limit of neurotransmitter: two ways
1) PREsynap realese neurotransmitter and inhibit synthesis
2) POSTsynap release chemical, travel back to pre to inhibit any release of neurotransmitter
AFTER SYNAPTIC, NEUROTRANSMITTER MUST BE REMOVED
